In general, television cameras for broadcasting input light from a view field into a color separation prism in order to obtain three separate, high quality, color-component images. A CCD array is then employed for each separated color component in order to obtain image information for that color component. In addition, television cameras are normally designed to employ a zoom lens for imaging objects onto the three CCD arrays. The aspect ratio (the ratio of the image width to height) for regular television viewing is fixed, and is 4:3.
However, a broadcasting format commonly known as high definition television, or HDTV, has been in market demand in recent years. The aspect ratio of the TV image in this format is 16:9. Therefore, when the height of the image remains the same as when using an aspect ratio of 4:3, with HDTV format the horizontal width of the image increases by a factor of 1.3333, and the diagonal measurement of the image increases by a factor of 1.2238.
As a result, if one were to attempt to use a zoom lens designed for regular TV (i.e., where the aspect ratio is 4:3) for HDTV (where the aspect ratio is 16:9), the illuminating beam of light from the lens would provide an image that is too small, in that the image would not fill the CCD array. From a different viewpoint, one could say that a zoom lens for regular TV is insufficient for HDTV use because the focal distance of the zoom lens is too short to fully illuminate the wider format of the HDTV image sensors.